Prevention of corrosion



Patented June 2, 1953 PREVENTION OF CORROSION .lohn Walter Nelson, Lansing, Ill., assignor, by mesne assignments, to Sinclair Oil and Gas Company, Tulsa, Okla., a. corporation of Maine No Drawing. Application December 19, 1950, Serial No. 201,691

2 Claims.

My invention relates to the prevention of corrosion in oil wells. In particular, I have found that carboxy acids obtained by the controlled oxidation of microcrystalline wax when added to well fluids in exceedingly small proportions act to effectively inhibit the rusting of the metallic equipment in the well. The crude product so obtained also possesses favorable rust-inhibiting properties when transported through'connecting pipe lines to the refinery.

Some degree of corrosion takes place in the metallic equipment of practically all oil wells and in certain environments corrosion may reach costly proportions. The casing, tubing and rod strings are subject to corrosive effects. The sucker rods and sucker rod boxes which operate under heavy cyclic load conditions are particularly susceptible to failure through corrosion fatigue. As a result of corrosion, costs may be greatly increased because of the necessity of pulling the well sucker rods and tubing string to overhaul or because of replacement of the equipment retired. Indirect costs in terms of production losses while replacing such pipe string sections and other equipment may also prove to be considerable.

Recognition of the oil well corrosion problem is comparatively new. However, the most effective method of corrosion control appears to reside in the use of chemical inhibitors. Such chemicals have the distinct advantage over other methods in that all parts of the well fluid system can be protected.

I have found that the corrosive effects of the well fluids on metallic surfaces can be substantially reduced, indeed in many cases practically eliminated, by introduction of an exceedingly minute proportion of carboxy acids obtained by the controlled oxidation of microcrystalline wax. The microcrystalline wax oxidate I use is prepared by oxidation with at least the sto-ichiometric amount of oxygen of sweet West Texas microcrystalline wax, containing 34 to 55 carbon atoms per molecule, at 230 to 240 F., in the presence of about 1% by weight of potassium permanganate (KMI104) as a catalyst, to a saponification number of about 157, according to the methods described in my copending applications, S N. 148,729 and S. N. 148,730, filed March 9, 1950, and S. N. 157,177, new Patent No. 2,610,974, filed April 20, 1950. In use the microcrystalline wax oxidate appears to form a protective layer over the metallic surface and thus prevents attack on the metal surfaces by the corrosive elements of the crude oil. It has a low solubility in water.

Besides affording remarkable protection against corrosion, the microcrystalline wax oxidate as employed is characterized by considerable ease in handling. In addition, the inhibitor does not have any toxic or other injurious effects on personnel. Oil production is not interfered with. such as by the formation of undesirable clogging or contaminating materials, either at the Well or later at the refinery, due to the fact that the microcrystalline wax oxidate is chemically very close to crude oil and consequently no contaminants are introduced into the well. And although my inhibitor is polar in nature because of its high molecular weight and long chain structure, it is extremely oil soluble and presents no emulsion problems. Further, since the inhibiting agent of my invention is essentially a simple oxidate of a very low-cost microcrystalline wax produced in large quantities in the dewaxing of heavy lube oils, it too can be produced and sold commercially at a very low figure. As a result, I am able to provide for substantial elimination of the damaging effects of corrosion by the use of a material of petroleum origin which is easily and safely handled and presents no contamination or emulsion problems and which will afford a substantial economic saving to present users of oil well corrosion inhibitors.

The efiective proportion of microcrystalline wax oxidate I employ is in the range approximating 0.2 to 2.0 pints per one thousand barrels of well fluid, i. e. crude oil and brine, with the upper limit being an arbitrary figure due to economic considerations. The inhibitor is added to the well fluids by merely injecting the desired amount down the annulus between the production tubing and casing. The crude product so obtained also displays favorable rust-inhibiting properties when transported through connecting pipe lines to the refinery. In the practice of my invention, I customarily employ the microcrystalline wax oxidate for convenience as a concentrate in oil solution. The oil concentrate may be stabilized by inclusion of a miscible polar solvent. A typical oil solvent may be an aromatic type petroleum solvent representing, for example, a heavy distillate cycle oil boiling between about 400 and 600 F.

As I have stated, considered on an oil-free basis, the effective amount of the microcrystalline wax oxidate employed is between 0.2 to 2.0 pints per one-thousand barrels of well fluid. Expressed in another way, this is equivalent to about 0.6 to 3.0,parts per million. Less than the minimum amount is generally ineffective in sub stantially reducing corrosion effects while over about 2.0 pints per 1000 barrels is unnecessary and wasteful of the inhibitor. Generally, I contemplate treating wells producing sour crudes, that is well fluids containing relatively large amounts of sulfur or sulfur compounds, since such wells present the majority of corrosion problems.

The actual amount of inhibitor employed within the above range is ordinarily directly related to the corrosiveness of the well fluid, the resistance of the metallic surfaces to corrosion and the production rate. In particular, flow interruptions and varying temperatures and pressures are capable of effecting corrosion considerably. Of course, the actual measure of corrosion, and therefore regulation of inhibitor concentration, can be determined in the last analysis by the actual deterioration in the physical condition of the metallic surfaces involved. However, it may not be practical to rely on such visual inspections since the damage is then already effected. Accordingly, metal test blanks may be used for insertion into the well stream and removed and examined at periodic. intervals. Direct measurement of the well fluid acidity is also-possible. Or ameasure of the iron content of the well fluid may be made since this is an indication of the metal lost through corrosion.

The following examples are offered to more clearly illustrate the nature and effectiveness of microcrystalline wax oxidate and resulting products according to my invention. However it must be: realized that the tests of the examples were run ona specific well and that the extreme variations foundamong, wellfiuids and rates and conditions of production of oilwel ls in the same and different fields are factors to be considered in drawing. any conclusions therefrom.- Also it. is well known that a'particular inhibitor may show superior anti-corrosive properties over those shown by other corrosion inhibitors in aparticular Well or field.and show inferior anti-corrosive properties to the' same other corrosion inhibitors in another well orfield. Consequently oil well corrosion inhibitors are customarily selectedfor use in a particularwell or field according-to the conditions in that well. or field, and eventhen the superiority ofa particular inhibitor over other inhibitors is unpredictable.

I compared the microcrystalline. wax oxidate with three oil wellcorrosion inhibitors two of which: appeared tobe among the most widely accepted of the inhibitors presently on the market, and the other a newproduct. These'three inhibitors were formaldehyde and substanceswhich I shall refer to as inhibitor A and inhibitor Formaldehyde. apparently functions by conversion of CHzO to CHzS, which polymerizes and coats steel surfaces. But this thioformaldehyde polymer has two objectionable qualities. It is a rubbery polymer which accumulates. in water drawofi lines particularly when a small. volume ofwater is produced with the. crude. Only when a large volume of'water is produceddoes the rub-'- bery. polymer washout so that. there is no objectionable amount of plugging. F'urther',. both the formaldehyde and thi'oformal'dehyde polymersare objectionable to field personnel. Although individuals difi'er greatly; some develop an. annoying skin rash after contact with the polymer.

The composition. of 'i'nhibit'oriA is not definitely known to me. although it: appears" to be an" oil 4 solution of a nitrogen base compound such as an imidazoline or salt thereof. Inhibitor A analyzes as follows:

Gravity 15.8 Acid No 20.7 Saponification No 23.8 Nitrogen, per cent 2.92 Phosphorus Nil Sulfur, per cent 0.22 Chlorine, per cent 0.042 Phenol No 46.4 (con) Ash ($04,) 0.05 Iron, per cent 0.0'7

Inhibitor A appears to form a heavy greaselike layer on the well tubing which retards contact between the metal and the corrosive fluids. But this grease layer sometimes is so hard that it catches in the teeth of fishing tools and the tools must be cleaned before they will function properly.

Inhibitor B is an. oil solution of commercially used sulfonate-type inhibitor of the following test" characteristics.

Gravity API s 28.0 Flash F' -s 385 Fire F 445 Viscosity at 100 SUS .s 416 Viscosity at 130 SUS -l 163 Viscosity at 210 SUS 49.2 Viscosity index Color 62.. 4% Nitrogen (per cent) 0.265

Acid Number 9".0

Sulfur (per cent) 0160 EXAMPLE I I first compared the microcrystalline was: oxidate with inhibitor'A by means of a stirring type laboratory'rust test, usingthe'equipment specified lVIicrocrystdlline p Wax Oxidate Inhlbltor A Amount; Wt. Percent in fluid i 1, Visual r 7 Visual LCLd. Rating l\l.d.d. I Ratihg 0.01' 50 D 242 E 0.02; 33 G 173' E The visual rating was-based on a 3+ whenonly 0-;25to-5' percent of the surface'arearusted; B when. 5 3025 per cent rusted; C when-25to50 percentrusted; D when 50 to 75- per cent rusted; and. E for 75 to-'per cent surface area rusting. Ablankcoupon under test conditions received an E rating and-corrosion from weight loss measurements was 224 m; d; d.

EXAMPLE II I then teste'd the microcrystalline wax oX'ida-te in an actual producingwelliin comparisonto in;

hibitor B. The general operating characteristics of the producing well, which I have indicated as Well No. 1 are given below.

General operating characteristics of well No. 1

Pumping Yes Production, bbls./day 420 Gas Small and vented Oil, bbls./day 20 Oil per cent 4.8 Sulfur, weight per cent 0.21 Brine, bbls./day 400 Total solids, p. p. m 37,070 Total hardness, p. p. m 1,439 Chlorine, p. p. m 21,440 pH 7.35 Per cent of total production 95.2 Temperature at well head F 105 Depth, top 3,260 Depth, bottom 3,296

Inhibitor B was first used as the corrosion inhibitor in the well. Five gallons of the inhibitor were added to the well down the casing annulus and recirculated with well fluid for five to twelve hours to assure even inhibitor distribution. Daily additions in the amount of one quart every other day of production were added by injection into the annular space between the production tubing and easing. Corrosion in the Well was then measured for the inhibitor over a period of forty-two days by placing weighed test coupons in the delivery lines from the well to the storage tanks.

The inhibitor employed in the well was then changed to the microcrystalline wax oxidate. For the changeover five gallons of inhibitor, made up as a solution of 12 weight per cent microcrystalline wax oxide, 78.5 weight per cent petroleum solvent, and 9.5 per cent isopropanol were added to the well down the casing annulus and recirculated with well fluid for five to twelve hours to assure even inhibitor distribution. One quart of the solution was added to the oil well every other day. This was at the rate of about 0.24 pint of microcrystalline wax oxidate on the oil free basis per 1000 barrels of well fluid.

The weight losses from the coupons from both tests were then converted to m. d. d. The results show that the average weight loss in milligrams of corrosion per square decimeter of surface per day, was 13.2 m. d. d. for inhibitor B and 3.1 m. d. d. for the microcrystalline wax oxidate. Further, there was less of the pitting type of corrosion attack on the test coupons where the microcrystalline wax oxidate was used.

Inhibitor B, Milmcrystal' Wt. Loss,

Test Period, Days M. d. d.

NI sw m...

Weight losses on corrosion test coupons usually give some indication of corrosion severity in a well, but much greater reliance must be placed on the number and frequency of tubing breaks and consequent well pulling operations during a given period of time. The well pulling records for Well No. 1 are presented below:

Well pulling record Well No. 1

Time with no inhibitor 13 months Number of pulling jobs 12 Pulling jobs per year at this rate 11 Time with formaldehyde 42 months Number of pulling jobs 36 Pulling jobs per year at this rate 10 Time with inhibitor A 2 months Number of pulling jobs 4 Pulling jobs per year at this rate 24 Time with inhibitor B 6 months Number of pulling jobs 4 Pulling jobs per year at this rate 8 Time with microcrystalline wax oxidate 5 months Number of pulling jobs 3 Pulling jobs per year at this rate 7 1 This figure is probably not reliable because of the short time element.

I claim:

1. In the production of oil from wells, the step of introducing into the well fluid 0.2 to 2.0 pints, calculated on the oil free basis, per 1000 barrels of well fluid, of a mixture of high molecular weight wax acids produced by substantially complete oxidation of microcrystalline wax containing 34- 55 carbon atoms per molecule, which mixture is characterized by extreme water insolubility and by a saponification number less than about 200, and which mixture predominates in monocarboxylic acids having an apparent chain length exceeding 18 carbon atoms per molecule.

2. Crude oil to which favorable rust inhibiting properties have been imparted by the addition of 0.2 to 2.0 pints, calculated on the oil free basis, per 1000 barrels of crude, of a mixture of high molecular weight wax acids produced .by substantially complete oxidation of microcrystalline wax containing 34-55 carbon atoms per molecule, which mixture is characterized by extreme Water insolubility and by a saponification number less than about 200, and which mixture predominates in monocarboxylic acids having an apparent chain length exceeding 18 carbon atoms per molecule.

JOHN WALTER NELSON.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,349,044 John May 16, 1944 2,373,787 Sharp Apr. 17, 1945 2,383,033 Adams Aug. 21, 1945 2,510,771 Bond June 6, 1950 

1. IN THE PRODUCTION OF OIL FROM WELLS, THE STEP OF INTRODUCING INTO THE WELL FLUID 0.2 TO 2.0 PINTS, CALCULATED ON THE OIL FREE BASIS, PER 1000 BARRELS OF WELL FLUID, OF A MIXTURE OF HIGH MOLECULAR WEIGHT WAX ACIDS PRODUCED BY SUBSTANTIALLY COMPLETE OXIDATION OF MICROCRYSTALLINE WAX CONTAINING 3455 CARBON ATOMS PER MOLECULE, WHICH MIXTURE IS CHARACTERIZED BY EXTREME WATER INSOLUBILITY AND BY A SAPONIFICATION NUMBER LESS THAN ABOUT 200, AND WHICH MIXTURE PREDOMINATES IN MONOCARBOXYLIC ACIDS HAVING AN APPARENT CHAIN LENGTH EXCEEDING 18 CARBON ATOMS PER MOLECULE. 